Various compositions (print-out compositions) capable of being discolored by light exposure to be visually distinguishable in unexposed portions from exposed portions are known, as described, for example, in J. Kosar, Light-Sensitive Systems, pages 358-401, published by J. Wiley and Sons, New York, 1965.
Also, the important application fields of these compositions are light-sensitive lithographic printing plates, photoresists, etc., and hence it is very advantageous to be able to visually distinguish these portions before development after the image exposure. See Japanese Patent Application (OPI) No. 13780/80 corresponding to European Pat. No. 5380, 74728/79 corresponding to U.S. Pat. No. 4,232,106 and 8128/78 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
That is, in the case of repeatedly printing out various originals by printing out a light-sensitive lithographic printing plate, a duplicated print-out on an already printed out portion can be prevented by using a print-out composition. Also, if a print-out composition is used for a photoresist for the production of a print base plate, it can be seen before development whether or not a photomask is correctly disposed, and the existence of any defects on the exposed portions can be easily determined.
Particularly effective print-out compositions are the compositions of organic polyhalogen compounds or other photooxidizing agents and various leuco dyes as disclosed, for example, in Photogr. Sci. Eng., Vol. 5, pp. 98-103 (1961) and U.S. Pat. No. 3,042,515.
Such known compositions give a high color density and clear images but have a fault of being easily discolored by exposure to air (or oxygen). Thus, it has been attempted to add various antioxidants to overcome this fault (see, for example, U.S. Pat. Nos. 3,042,515 and 4,066,459 and Japanese Patent Application (OPI) No. 31581/81 corresponding to U.S. Pat. No. 3,827,887.
However, when these compositions with additives are stored for a long period of time, or are stored under conditions of high temperature and high humidity, the compositions still become discolored, and hence further improvement of such print-out compositions has been desired.